1. Field of the Invention
This invention relates to a film projection apparatus for projecting an image formed on a film and more particularly to a focus adjustment mechanism and a film holding member of the film projection apparatus.
2. Description of the Related Art
The conventional film projection apparatus is arranged as shown in FIGS. 16 and 17. In the case of the film projection apparatus shown in FIG. 16, a light flux emitted from a projection light source 2, together with reflection light obtained with the light flux reflected by a reflection mirror 1, illuminates through condenser lenses 3 and 4 a film F which is disposed within a film holding member 5. A light image which comes from the film F thus illuminated is projected onto the original-board glass 9 of an image reading device through a projection lens 6 and a Fresnel lens 8. In making focus adjustment, the operator of the apparatus rotates a focus adjustment knob 11 while keeping the projected image in sight. A desired in-focus state is obtained by rotating the focus adjustment knob 11 to move via an intermediate gear 10 a lens barrel 7 which holds the projection lens 6. FIG. 17 shows this film projection apparatus in an oblique view.
With the conventional apparatus arranged in the above-stated manner, however, it has been not easy for the operator to make focus adjustment. Therefore, an image reading process has occasionally been performed to give a blurred image as a result of inadequate focus adjustment. In other words, in order to obtain a high-quality image, the operator must bring the apparatus into an adequate in-focus state by rotating the focus adjustment knob 11 while watching the image projected on the Fresnel lens 8, as shown in FIG. 17. An in-focus state can be easily attained without fail if some suitable high-contrast part that is usable as a criterion for a discrimination between an in-focus state and a defocus state exists within the projected image. However, in a case where the projected image does not have such a suitable high-contrast part, the image quality might become hardly acceptable as the apparatus tends to be in a defocus state after focus adjustment under such a condition, depending on the skill of the operator.
Further, in a case where a negative film original is projected, every bright part of the real image is dark, because the image on the film is reversed. Then, even if a suitable high-contrast part is included in the projected image, the focus adjustment work is much more difficult than in the case of a positive film original. Therefore, in such a case, the probability of a failure to obtain an acceptable image quality further increases.
With respect to the structural arrangement of the film holding member 5, the member 5 consists of an upper holding plate 13 and a lower holding plate 14, as shown in FIG. 18. These plates 13 and 14 are rotatably mounted on a hinge shaft 15 respectively by means of hinge parts 13a and 14a. A negative film original F is arranged to be sandwiched in between the upper and lower holding plates 13 and 14. Further, the negative film original F is longitudinally positioned by abutting one longitudinal end thereof on the longitudinal guide 14d of the lower holding plate 14 and transversely positioned by transverse guides 14b and 14c, which are opposed to each other on the lower holding plate 14. The upper holding plate 13 is provided with escape holes 13b, 13c and 13d for receiving the guides 14b, 14c and 14d.
The operator first turns the upper holding plate 13 around the hinge shaft 15 to open the film holding member 5. The negative film original F is set in between the opposed transverse guides 14b and 14c while abutting one longitudinal end of the film original F on the longitudinal guide 14d. The setting work on the negative film original F is completed with the upper holding plate 13 closed by turning the upper holding plate 13 around the hinge shaft 15.
However, with the conventional film holding member 5 arranged as described above, the negative film original F cannot be adequately positioned sometimes in the transverse direction and is thus set in a state of deviating from a correct setting position, depending on the condition of the film original F. In the worst case, the negative film original F is deformed by the setting work. More specifically, in cases where the negative film original F is, for example, curved in a concave shape as shown in FIG. 19, if the curving amount S exceeds the height h of the transverse guide 14c of the lower holding plate 14, the negative film original F might be set in a state of overriding the transverse guide 14c. If the film holding member 5 is closed by turning the upper holding plate 13 around the hinge shaft 15 with the negative film original F in that state, the negative film original F is set in a deflected state. In the worst case, the negative film original F is deformed under such a condition.
If the negative film original F is either in a flat state or in a convex shape, instead of the concave shape shown in FIG. 19, the film original F is safe from the above-stated trouble. However, the negative film original F is formed by coating a transparent polyester film with an emulsion. Therefore, the negative film original F might be caused to act like a bimetallic material by a difference in expansion coefficient between two matters due to ambient temperature and humidity. The negative film original F thus tends to curve in an arbitrary direction and thus might result in the concave shape to hinder adequate setting work and to be deformed by the setting work.